Detection and removal of blemishes in digital images utilizing original images of defocused scenes

ABSTRACT

A method automatically corrects dust artifact within images acquired by a system including a digital acquisition device including a lens assembly and a translucent lens cap. Multiple original digital images are acquired with the digital acquisition device. Probabilities that certain pixels correspond to dust artifact regions within the images are determined based at least in part on a comparison of suspected dust artifact regions within two or more of the images. Probable dust artifact regions are associated with extracted parameter values relating to the lens assembly when the images were acquired. A statistical dust map is formed including mapped dust regions based on the determining and associating. Pixels corresponding to correlated dust artifact regions are corrected within further digitally-acquired images based on the associated statistical dust map.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional patent application60/773,714, filed Feb. 14, 2006, which is incorporated by reference, andis related to a family of patent applications filed on the same dayincluding 2005/0068450, 2005/0068451, 2005/0068452, 2005/0078173,2005/0068448, 2005/0068445, 2005/0068446, and 2005/0068447, which arealso incorporated by reference, as is U.S. Pat. No. 6,035,072.

BACKGROUND

1. Field of the Invention

This invention related to digital photography, and in particular,automated means of removing blemish artifacts from de-focused imagescaptured and digitized in a digital process.

2. Description of the Related Art

Many problems are caused by dust in particular and blemishes in generalon imaging devices in general and digital imaging devices in particular.In the past, two distinct forms of image processing included providingmeans to detect and locate dust, scratches or similar defects andproviding means to remedy the distortions caused by the defects to animage. It is desired to have an advantageous system that combines thesefunctions, and can automatically detect and correct for the effects ofdust, scratches and other optical blemishes.

Dust has been a problem in scanning devices for a long time. Variousaspects of the scanning process, enhanced by image processing techniqueswhere appropriate, have been employed to provide means for the detectionof dust or defects relating to document or image/film scanners. Thesedevices form an image by moving a 1D sensor pixel array across adocument platen, or in some cases, the document platen withdocument/image, is moved across the sensor array. The physics andimplementation of these devices differ significantly from those of afield-based sensor or camera-style device. It is desired particularly tohave dust and/or blemish detection and correction techniques forfield-based or camera-style acquisition devices.

Image correction has been studied in relation to display devices, outputapparatuses such as printers, and digital sensors. Image correction ofdust artifacts can be used to recreate missing data, also referred to asin-painting or restoration, or undoing degradation of data, which stillremains in the image, also referred to as image enhancement. It isdesired to have a system including a digital camera and an externaldevice or apparatus that can facilitate a defect detection and/orcorrection process involving sophisticated and automated computerizedprogramming techniques.

SUMMARY OF THE INVENTION

A digital image acquisition device is provided which includes an imageacquisition sensor, a shutter, optical elements for focusing an image onthe sensor, an aperture disposed between said optical elements and saidshutter, a translucent lens cap which defocuses images when in place,and digitally-embedded programming. The device is arranged toautomatically capture a calibration image of a de-focused scene when theshutter and the aperture are open. A map of defects is derived from thecalibration image acquired by the sensor when illuminated by ambientlight.

The device may include a trigger for automatically acquiring ade-focused calibration image which is arranged to automatically detectwhether the translucent lens cap is in place as a pre-requisite fortriggering capture of the defocused calibration image. The trigger maybe arranged to trigger image capture based at least in part on timeinterval, change of lens, or amount of images taken, or a combinationthereof. The trigger may include programming for analyzing whether theimage is sufficiently de-focused as a pre-requisite for capture of thede-focused calibration image. The trigger may be arranged to initiatecapture of a plurality of de-focused calibration images of the scenewithin a certain time frame.

A further digital image acquisition device is provided which has nophotographic film. The device includes an optical system, a processorand one or more storage devices for programming the processor to controlthe camera to perform a method of automatically correcting dust or otherblemish artifact regions within acquired images. The method includesacquiring one or more original digital images through a translucent lenscap disposed along an optical path between an object and one or morecomponents of the optical system including a digital sensor.Probabilities that certain pixels correspond to dust or other blemishartifact regions within the one or more original digital images aredetermined. The dust or other blemish artifact regions are associatedwith one or more extracted parameters relating to the optical systemwhen the one or more original digital images were acquired. Astatistical dust map is formed including mapped dust or other blemishregions based on the dust or other blemish artifact probabilitydetermining and associating. Pixels are corrected corresponding to dustartifact regions within the one or more original images based on theassociated statistical dust map.

The one or more original images may include original images ofde-focused scenes.

A plurality of individual probabilities may be statistically combinedbased on regions within two or more images. Probabilities may bedetermined that certain pixels correspond to regions free of dust orother blemishes within the images based at least in part on a comparisonof suspected dust artifact regions within one or more of the images.Certain suspected dust or other blemish artifact regions may beeliminated as having a probability below a first threshold value.Certain probable dust or other blemish artifact regions may be judged ashaving a probability above a second threshold value such as to besubject to the correcting.

The one or more extracted parameters may include aperture size or focallength or both.

The method may further include digitally-acquiring additional imageswith the digital acquisition device, repeating the determining andassociating, and updating the statistical dust map including updatingthe mapped dust or other blemish regions based on the additional dust orother blemish artifact determining and associating. The determining mayinclude dynamically updating the probabilities based on comparisons withsuspected equivalent dust artifact regions within the additionaldigitally-acquired images.

It may be validated whether additional digitally-acquired images havenon-contradicting probability data that certain pixels correspond todust or other blemish artifact regions within the additionaldigitally-acquired images prior to correcting pixels corresponding tocorrelated dust artifact regions within additional digitally-acquiredimages based on the associated statistical dust map.

The dust or other blemish artifact determining may include:

(I) loading the statistical dust map;

(II) loading extracted parameter information of a present image;

(III) performing calculations within the statistical dust map havingextracted parameter variable-dependencies; and

(IV) comparing dust artifact detection data with the extracted parameterdependent statistical dust map data.

The dust or other blemish artifact determining may also include:

(I) loading the statistical dust map;

(II) loading extracted parameter information of a present image;

(III) performing a calculation for relating the statistical dust mapwith the present image according to a selected value of an extractedparameter which is otherwise uncorrelated between the present image andthe dust map; and

(IV) comparing dust artifact detection data with the now correlatedstatistical dust map data.

The method may further include sorting dust or other blemish artifactdistribution data within the dust map according to meta-data.

The digital acquisition device may capture the images from film images.

A method is also provided for automatically correcting dust or otherblemish artifacts within images acquired by a system including a digitalacquisition device including a lens assembly is provided. The methodincludes acquiring multiple original digital images of a defocused scenewith the digital acquisition device having a translucent lens cap inplace. Probabilities that certain pixels correspond to dust or otherblemish artifact regions within the images are determined based at leastin part on a comparison of suspected blemish artifact regions within twoor more of the images. Probable blemish artifact regions are associatedwith one or more values of one or more extracted parameters relating tothe lens assembly of the digital acquisition device when the images wereacquired. A statistical dust or other blemish artifact map is formedincluding mapped blemish regions based on the dust or other blemishartifact determining and associating. Pixels corresponding to correlateddust artifact or other blemish regions are corrected within furtherdigitally-acquired images based on the associated statistical dust map.

The image correction method may be automatically performed within adigital camera that includes an optical system including one or morelenses, a shutter and a translucent lens cap, a sensor array, processingelectronics, and a memory. The image correction method may also beperformed at least in part within an external processing device thatcouples with a digital camera that includes the optical system and thesensor array to form a digital image acquisition and processing systemthat also includes the processing electronics and the memory. Theprogramming instructions may be stored on a memory within a cameraand/or the external device which performs the image correction method.The digital acquisition device may capture images from film images, andthe digital acquisition device may include a digital camera.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a main workflow of a dust removal process inaccordance with a preferred embodiment.

FIG. 2 a illustrates the creation of a dust map.

FIG. 2 b illustrates an alternative embodiment of the creation of abinary dust map.

FIG. 3 outlines a correlation of a dust map to image shootingparameters.

FIG. 4 a illustrates a procedure for detecting and removing dust fromimages in accordance with a preferred embodiment.

FIG. 4 b illustrates reconstruction in-painting of dust regions.

FIG. 4 c illustrates the occurrence of dust in a picture with high edgeinformation.

FIG. 4 d illustrates the numerical gradient in an image.

FIGS. 4 e-4 f illustrate a spiral procedure of in-painting from theperiphery inwards.

FIG. 5 illustrates a quality control method of checking the dust map.

FIGS. 6 a-6 f represents an optical geometry of a lens that may be usedin accordance with a preferred embodiment:

FIGS. 6 a, 6 b and 6 c represent three lenses with the same, fixed,focal distance, with the same focal number, but with differentconstructions.

FIG. 6 d illustrates the concept of an exit pupil and the distance toit.

FIG. 6 e illustrates intersections of the principal ray with windows andimage plane, which is preferably approximately the sensor plane.

FIG. 6 f illustrates the shift of one dust spec in comparison with ashift of another dust spec in an image.

FIG. 6 g illustrates the capturing of images of de-focused scenes when atranslucent lens cap is in place.

FIGS. 7 a-7 f generally illustrate effects of dust on the creation of animage using a known optical system:

FIG. 7 a illustrates an influence of a dust particle located on theinput surface of the window on the beam converging towards the imagingpoint.

FIG. 7 b illustrates a side view of the rays as obscured by dust as afunction of the aperture.

FIG. 7 c illustrates a frontal projection of the rays as obscured by adust as a function of the aperture.

FIG. 7 d and FIG. 7 e illustrate a power distribution map of the samedust spec as manifested in different f-stops.

FIG. 7 f illustrates an effect of the change in focal length on the areaobscured by the dust.

FIG. 8 illustrates an adjustment of the dust map based on aperture.

FIG. 9 illustrates an adjustment of a dust map based on focal length.

FIG. 10 illustrates a process of estimating based on empirical data thevalues of the parameters in the formulae that defines the change in dustas a function of change in focal length.

FIG. 11 illustrates a process of estimating based on empirical data thevalues of the parameters in the formulae that defines the change in dustas a function of change in aperture.

FIG. 12 illustrates a further process in accordance with anotherembodiment.

BRIEF DESCRIPTION OF TABLES

Table 1 lists parameters in mathematical formulations of the opticalsystem.

Table 2 lists potential Extracted Lens Parameters.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Some Definitions

Dust specs: The preferred embodiment takes advantage of the fact thatmany images may have repetitive manifestation of the same defects suchas dust, dead-pixels, burnt pixels, scratches, or other blemishes.Collectively, for this specification all possible defects of this natureare referred to in this application as dust-specs or dust defects, eventhough such defects may be caused by other sources of blemishes. Theeffects of those dust specs on digital images are referred to herein asdust artifacts.

Acquisition device: the acquisition device may be a multi-functionalelectronic appliance wherein one of the major functional capabilities ofsaid appliance is that of a digital camera. Examples include digitalcamera, a hand held computer with an imaging sensor, a scanner, ahand-set phone, or another digital device with built in optics capableof acquiring images. Acquisition devices can also include film scannerswith an area-capture CCD, as contrasted, e.g., with a line scanmechanism.

D-SLR: Digital Single Lens Reflex Camera. A digital camera where theviewfinder is receiving the image from the same optical system as thesensor does. Many D-SLR, as for SLR cameras have the capability tointerchange its lenses, this exposing the inner regions of the camera todust.

A few parameters are defined as part of the process:

-   N Number of images in a collection.-   Hidp Number of images for occurrence to be high dust probability.-   HSdp Number of recurring specs for label a region to be high dust    probability.-   p(hsdp) Probability threshold for high confidence of a dust spec.-   N dp Number of images to determine that a region is not dust.-   p(ndp) Probability threshold to determine that a region is not a    dust region.    Most likely Hidp<=HSdp-   I—is a generic image.-   I(x,y) pixel in location x horizontal, y vertical of Image I.-   pM is a continuous tone, or a statistical representation of a dust    map.-   dM is a binary dust map created form some thresholding of pM.

Mathematical Modeling of the Optical System

Prior to understanding the preferred embodiments described herein, it ishelpful to understand the mathematical modeling of the camera opticalsystem. With this modeling, the preferred embodiments may advantageouslyutilize a single dust map for dust detection and/or correctiontechniques rather than creating a dust map for each instance of dustartifact having its own shape and opacity depending on extractedparameters relating to the imaging acquisition process. With an abilityto model the optical system and its variability, a single map maysuffice for each lens or for multiple lenses, and for multiple focallengths, multiple apertures, and/or other extracted parameters asdescribed in more detail below.

In order to study the shadow of an object on a plane, it is helpful toconsider the following:

-   -   the illumination of the object (the spectral and coherent        characteristics of the light)    -   the shape of the object (including its micro-geometry)    -   the reflection and transmission properties of the object    -   the relative position of the object and the plane

The case of interest for defining the model of dust as it appears on thesensor, is that of an object close to the image plane of a lens, whichis a complex optical system, with natural light illumination. The objectshape and its reflection and transmission properties are practicalimpossible to model because no any specific information on the dustparticle is available. On the other side, because the dust particles aresmall, it is very probable to have the same reflection and transmissionproperties on their surfaces. The distance between the dust and thesensor, which is the image plane is small and is in the order ofmagnitude of fraction of a millimeter.

Some Definitions as to notations are now provided:

TABLE 1 Parameters in Mathematical Formulation of the Optical SystemPe - exit pupil position, the distance between the sensor, and the ExitPupil tw - thickness of the window, distance of dust to the image planef′- focal length of the objective f/#- focal number (u, v) - denote thecoordinate system of the input surface, having its origin in theintersection point with the lens optical axis. (x, y)- the dust positionon the image plane in the coordinate system in the image plane with theorigin in the intersection point with the lens optical axis. l(x, y)- bethe value of the irradiance in the image point (x, y) D - is the exitpupil diameter h₀ is the distance of the objects on the dust plane tothe center of the optical path h is the distance form the object to thecenter of the optical axis h_(k) is the distance of dust spec k on thedust plane to the center of the optical path

FIGS. 6 a, 6 b and 6 c represent three lenses with the same, fixed,focal distance, with the same focal number, but with differentconstructions. The first construction, in FIG. 6-a is the most common.The second in FIG. 6 b is specific for the lenses used in metrology.This type of lens is called telecentric in the image space. The third inFIG. 6 c construction is rarely found in optical systems, but notimpossible.

FIG. 6 d illustrates the concept of an exit pupil and the distance toit. The exit pupil distance, 644, is the parameter that defines thisproperty, and represents the distance from the secondary principalplane, 646, of the lens and the intersection of the axis of the lightcone and optical axis of the lens. The focal distance 644 represents thedistance form the secondary principal plane to the object plane.

In the case of the second type lens, as defined in FIG. 6 b, the exitpupil position is at infinity. In the first and third case, FIGS. 6 aand 6 c respectively, the intersections of the light cone with the dustplane are ellipses. In the case of the second lens type, FIG. 6 b theintersection of the light cone with the dust plane is a circle.

In the case of zoom lens, the exit pupil position can be constant (atinfinity), or can vary significantly, depending on the construction ofthe lens.

This information about the exit pupil is usually not public because, ingeneral, it is not useful for the common user of photographic or TVlenses. However, this information can be readily available with somemeasurements on an optical bench. Alternatively, this information can beachieved based on analysis of dust in the image.

FIG. 6 e illustrates the Intersections of the principal ray with windowsand image plane, which is the sensor plane. This figure illustrates thevarious parameters as defined in Table 1. FIG. 6 f illustrates the shiftof one dust spec in comparison with a shift of another dust spec in animage.

FIG. 7 a describes the influence of a dust particle (obscuration)located on the input surface of the window (obscuration plane), on thebeam converging towards the imaging point.

FIG. 6 g illustrates the capturing of images of de-focused scenes when atranslucent lens cap is in place. With the lens cap removed, an objectmay be in focus at the image plane of a camera's detector D. With thetranslucent lens cap on, however, light rays traveling through thetranslucent lens cap are disrupted resulting in a de-focused image atthe detector D.

In the embodiment of FIG. 6 g, the camera used to capture the image isarranged to receive a translucent lens cap. The translucent lens capserves to provide an ideal source of a defocused (smooth) image to thecamera sensor D in order to enable the camera to capture an image of adefocused scene or object, thereby producing a simpler image or set ofimages to be referenced for dust map calculations.

In such an embodiment, the camera is arranged to automatically detectwhether the lens cap is in place in order to trigger the capture of thedefocused image. In such an embodiment, the dust map may be generatedperiodically and automatically, without the user having to perform anycalibration action. The trigger to automatically acquire such image forthe dust map can be time interval, change of lens, amount of imagestaken, replacement of lens cap, or combinations of these or otherparameters.

Alternatively, the camera may be arranged to detect if a lens cap is onprior to capturing an image and analyzing if the image captured ishighly defocused.

Alternatively, the camera is arranged to automatically acquire an imageand determine if the image is of a generally de-focused scene.Alternatively, captured images may be examined to determine whether theyare of a generally de-focused scene suitable for dust calibration. Inany case, once the camera is imaging a defocused scene, the camera isarranged to capture a plurality of images of such a scene within acertain time frame. This embodiment may include a camera arranged toperform any combination of these de-focused image-capturing techniques.

FIG. 7 b illustrates the side view of the rays as obscured by a dust asa function of the aperture.

FIG. 7 c illustrates the frontal projection of FIG. 7-b, of the rays asobscured by a dust as a function of the aperture.

FIG. 7 d and FIG. 7 e illustrates a power distribution map of the samedust spec as manifested in different f-stops, namely a relative openaperture f-9 for FIG. 7 d and a closed aperture, namely f-22 and higher,in FIG. 7 e. One can see that the dust spot as recorded with the closedaperture is much sharper and crisper.

The dust particle is situated in the window plane, and totally absorbingor reflecting the portion of the beam (S2) that normally reaches theimage point (P).

Let I(x,y) be the value of the irradiance in the image point (x,y) inthe absence of the dust particle. Assuming that the energy in the exitpupil of the optical system is uniformly distributed, then, in thepresence of the dust particle, the I(x,y) will be reduced proportionallywith the ratio between the area of the intersection of the light beam(S1) with the clean zone of the window, and the whole area of the sameintersection (Sc).

Remember that Sc is a function of the lens f-number (f/#) and windowthickness t_(w), so the value of the real irradiance in the presence ofdust will be:

$\begin{matrix}{{I^{\prime}\left( {x,y} \right)} = {{I\left( {x,y} \right)}\frac{S\; 1}{Sc}}} & (4)\end{matrix}$or, by taking into account that S1=Sc−S2 and S2=area of intersectionbetween the dust particle and the illuminated area:

$\begin{matrix}{{I^{\prime}\left( {x,y} \right)} = {{{I\left( {x,y} \right)}\left( {1 - \frac{S\; 2}{Sc}} \right)} = {{I\left( {x,y} \right)}\left( {1 - \frac{S_{D\bigcap C}}{Sc}} \right)}}} & \left( {4a} \right)\end{matrix}$

Because the dust particle is small, the next assumption can be made forall the image points affected by a specific dust particle, the area Scremains constant.

In the case of the telecentric illumination, this assumption holds truefor all the image points.

With the assumption above, we can correlate the dust geometry, positionand shadow.

First of all, we now study the distribution of the irradiance on theinput plane of the window. The intersection of the conic beam with thisplane is generally an ellipse. The major axis of this ellipse is alongthe intersection of the plane mentioned above and the plane determinedby the image point and the optical axis of the lens.

The minor axis is:

$\begin{matrix}{b = {t_{w}\frac{D}{P_{e}}}} & (5)\end{matrix}$whereas the major axis is:

$\begin{matrix}{a=={t_{w}\frac{D}{P_{e}}\frac{1}{\cos\left( {{arc}\;{tg}\frac{h}{P_{e}}} \right)}}} & (6)\end{matrix}$where D is the exit pupil diameter, so:

$\begin{matrix}{D = \frac{f^{\prime}}{f/\#}} & (7)\end{matrix}$

In order to reach a complete formula of the irradiance distribution wenow stress the assumption that for all image points affected by a chosendust particle, “a” varies insignificantly. Let (u₀,v₀) be the point ofintersection of the principal ray with the plane mentioned above.

So, the characteristic function of the illuminated zone will be:C=C(u,v,u ₀ ,v ₀ ,f′,f/#,P _(e) ,t _(w))  (8)

Let D(u,v) be the characteristic function of the dust. Then, the centerof the cone intersection with the input plane of the window will begiven by (3).

Thus,

$\begin{matrix}{S_{D\bigcap C} = {\int_{R}{\int_{xR}{{D\left( {u,v} \right)}*{C\left( {u,v,u_{0},v_{0},f^{\prime},{f/\#},P_{e},t_{w}} \right)}\ {\mathbb{d}u}\ \overset{10}{\mathbb{d}v}}}}} & (9) \\{{I^{\prime}\left( {x,y} \right)} = {{I\left( {x,y} \right)}\left( {1 - \frac{\int_{R}{\int_{xR}{{D\left( {u,v} \right)}*{C\left( {u,v,u_{0},v_{0},f^{\prime},{f/\#},P_{e},t_{w}} \right)}\ {\mathbb{d}u}{\mathbb{d}v}}}}{Sc}} \right)}} & (10)\end{matrix}$which eventually, using the relation (3), yields:

$\begin{matrix}{{I^{\prime}\left( {x,y} \right)} = {{I\left( {x,y} \right)}\left( {1 - \frac{\begin{matrix}{\int_{R}{\int_{xR}{{D\left( {u,v} \right)}*{C\left( {u,v,{\left( {1 + \frac{t_{w}}{P_{e}}} \right)x},} \right.}}}} \\{\left. \ {{\left( {1 + \frac{t_{w}}{P_{e}}} \right)y},f^{\prime},{f/\#},P_{e},t_{w}} \right){\mathbb{d}u}\ {\mathbb{d}v}}\end{matrix}}{Sc}} \right)}} & (11)\end{matrix}$The terms (1+t_(w)/P_(e))x and (1+t_(w)/P_(e))y determine the “movement”of the dust shadow with the change of the focal distance and,implicitly, of the Pe, as explained later on in equation 13.In the case of the telecentric illumination:

-   -   Pe is infinite,    -   u0=x and v0=y.    -   the ellipse becomes a circle

Qualitatively, as described quantitatively in equation 11, the fall off,or the diminished effect of the dust on an image varies as follow: Thedust is becoming less significant as the aperture becomes larger, or thef-stop is smaller and the pixels are inversely affected based on thedistance of the pixel to the periphery of the dust.

FIG. 7 f illustrates the adaptation between the dust map and the imagebased on the focal length of the lens. In this figure one canqualitatively see that the area covered by the dust spec will be shiftedas a function of the focal length.

Also, information about the spatial distribution and/or orientation ofdust particles within the dust map may be used to assist withdetermining probabilities that regions are either dust or non-dust. Asan example, one could expect that a global average of the orientation ofelongated dust particles would average to zero. However, at a morelocalized level, charged and/or magnetized dust particles can tend toalign with similar orientations due to local dielectric forces. Thiseffect would be partly dependent on the size, overall shape distribution(round or more elongated) and the overall distribution (uniform orclumped) of the dust regions in the dust map. This can tend to beparticularly helpful when a decision is to be made as to whether toeliminate certain regions, e.g., most of the dust may be aligned in aradial direction relative to the center of the sensor, and thenparticles in a concentric alignment are less likely to be dust.

Given the definitions above, a more quantitative model can be deducted:

$\begin{matrix}{h = {{h_{0}\frac{1}{1 + \frac{t_{w}}{P_{e}}}} \cong {h_{0}\left( {1 - \frac{t_{w}}{P_{e}}} \right)}}} & (12)\end{matrix}$because the ratio t_(w)/P_(e) is small. Note that Pe has in common casesa negative value.

Let (u,v) denote the coordinate system of the input surface, having itsorigin in the intersection point with the lens optical axis. Similarly,let (x,y) be the coordinate system in the image plane with the origin inthe intersection point with the lens optical axis.

Thus, if the principal ray of the beam intersects the input window planein the point (u,v), the point in the image plane on the same principalray will be The inverse transformation of (2)

$\begin{matrix}{\begin{bmatrix}x \\y\end{bmatrix} = {\begin{bmatrix}{1 - \frac{t_{w}}{P_{e}}} & 0 \\0 & {1 - \frac{t_{w}}{P_{e}}}\end{bmatrix}\begin{bmatrix}u \\v\end{bmatrix}}} & (2)\end{matrix}$with the same assumption of a small tw/Pe ratio will be

$\begin{matrix}{\begin{bmatrix}u \\v\end{bmatrix} = {\begin{bmatrix}{1 + \frac{t_{w}}{P_{e}}} & 0 \\0 & {1 + \frac{t_{w}}{P_{e}}}\end{bmatrix}\begin{bmatrix}x \\y\end{bmatrix}}} & (13)\end{matrix}$FIG. 7 j depicts how points will shift as a function of the proximity tothe optical center. Basically the farther the dust is form the center,the larger the displacement is. However, the direction and size of thedisplacements can be estimated. At the same time, the closer the dustspot is to the center, the more its shape will change.

There are a few parameters that are not published. The distance, Tw, ofthe dust to the image plane is typically fixed for the camera and asingle measurement can achieve that.

The exit pupil distance may vary depending on the focal length of thelens, in particular for a zoom lens, the Exit pupil distance may not bemost likely fixed, and can vary up to a telecentric mode where thedistance is infinity.

However, such information can be empirically extracted by analysis ofimages taken by a known camera and lens, as illustrated below and inFIG. 7 e. In this case, knowledge of the effect of one dust spec can beused to calculate the shift for any other dust spec in the image.

In this figure a hypothetic zoom lens of 70 mm-210 mm is illustrated:

-   -   Pe-70 is the exit pupil position for the lens at 70 mm,    -   Pe-210 is the exit pupil location when the lens is at its        highest enlargement 210 mm.    -   k, is known dust    -   m is hypothetical dust    -   h_(k) is h for a specific dust particle k.

Knowledge of the shift of dust image (preferable near to one of thecorners of the image).

The equation (12)

$\begin{matrix}{h \cong {h_{0}\left( {1 - \frac{t_{w}}{P_{e}}} \right)}} & (12)\end{matrix}$

can be written for a specific dust particle (k) and underline thedependence with the focal distance,

$\begin{matrix}{{{h_{k}(f)} = {h_{0k}\left( {1 - \frac{t_{k}}{P_{e}(f)}} \right)}}{or}} & \left( {12\text{-}a} \right) \\{\frac{h_{k}(f)}{h_{0k}} = {\left( {1 - \frac{t_{w}}{{Pe}(f)}} \right)\mspace{14mu}{independent}\mspace{14mu}{from}\mspace{14mu} k}} & \left( {12\text{-}b} \right)\end{matrix}$So, if we know the evolution of the image of the “k” dust particle wecan find the evolution of the “m” dust image

$\begin{matrix}{{h_{m}(f)} = {\frac{h_{0m}}{h_{0k}}{h_{k}(f)}}} & \left( {12\text{-}c} \right)\end{matrix}$The problem with this formula is again we don't know the positions ofthe dust particles Writing the upper formula for a given focal distance,say f₀, we have

$\begin{matrix}{\frac{h_{0m}}{h_{0k}} = \frac{h_{m}\left( f_{0} \right)}{h_{k}\left( f_{0} \right)}} & \left( {12\text{-}d} \right)\end{matrix}$So, finally

$\begin{matrix}{{h_{m}(f)} = {\frac{h_{m}\left( f_{0} \right)}{h_{k}\left( f_{0} \right)}{h_{k}(f)}}} & \left( {12\text{-}e} \right)\end{matrix}$This relation does not need the exit pupil dependence, the thickness ofthe window and the dust position.Alternatively, given formula (13) and given an image where the dust canbe detected, one can calculate Pe as follows:

$\begin{matrix}{{\frac{x}{u} = {\frac{y}{v} = {1 + \frac{t_{w}}{P_{e}}}}}{or}} & \left( {13\text{-}a} \right) \\{P_{e} = {{\left( {1 + t_{w}} \right) \times \frac{u}{x}} = {\left( {1 + t_{w}} \right) \times \frac{v}{y}}}} & \left( {13\text{-}b} \right)\end{matrix}$In summary of the mathematical model of the optical system for dust, inthe general case, the way the image is affected by the dust depends on:

exit pupil position Pe thickness of the window tw focal length of theobjective f′ focal number f/# the dust position on the image plane (x,y)

This can be calculated by knowing the optical system's components:

-   -   a) the window thickness (tw),    -   b) the function Pe(f), and    -   c) the coordinates (u,v) of the dust if we want to determine the        dust image position on the image plane.

The main workflow of detecting and removing the dust from an image isillustrated in FIG. 1. The preferred embodiment is activated in fourdifferent cases. In general, this preferred embodiment works forremoving dust form a collection of images having the same acquisitiondevice. Specifically, a user may acquire a picture on her digital camera(as illustrated in Block 101). Alternatively (102), a user may open asingle image on a external device such as a personal computer, open(103) a folder of images on an external device or open a collection ofimages on a digital printing device (104).

The preferred embodiment then extracts the shooting parameters (120).Such parameters include, but not limited to data about: Camera name,Lens brand, lens type, focal length at acquisition, aperture range,aperture at acquisition.

In addition, some parameter, in particular on the lens and the cameramay be also stored in the device, which is the acquisition device suchas the digital camera or the processing device such as the personalcomputer or digital printer. Such information may include parameterssuch as exit pupil, exit pupil distance regarding the lens, or distanceof dust to sensor for the camera.

A table with such data may look like:

TABLE 2 Extracted Lens Parameters Field Example of data Category LensManufacturer Nikon lens Lens Type AF 24 mm-45 mm f 2.8-f 3.5 lens FocalLength 38 mm Acquisition data Aperture f-16 Acquisition data Dustdistance 0.156 mm Camera data Exit pupil 19 mm Lens data Exit pupildistance 230 mm Lens data

The dust map may also include meta-data that are different the list ofextracted parameters. Moreover, that which is described as beingextracted parameter dependent or encoded with extracted parameter valuedata or based on a value of an extracted parameter can be broadened toinclude other meta-data than just the extracted parameters listed inTable 2. For example, certain meta-data are dependent on parametersexisting at the time of acquisition of the image, and can becamera-specific or not. The amount of ambient light available willdepend on whether there is artificial lighting nearby or whether it is acloudy day. Discussion of meta-data as it relates to image acquisitionis found in more detail at U.S. patent application Ser. No. 10/608,810,filed Jun. 26, 2003, and is hereby incorporated by reference.

In the case that the system deals with multiple images (as defined in102, 103, and 104), the algorithm describes a loop operation on allimages (110). The first step is to open a dust map (130). If non exists(132) the system will create a new dust map (200) as further describedin FIG. 2. In the case that the system has a few dust maps (130) thesoftware will try to correlate one of the maps (300) to the image. Thisprocess is further illustrated in FIG. 3. In particular this correlationrefers to the adjustment of the shooting conditions to some acceptedstandard. The acquisition conditions in particular refer to the apertureand the focal length. The correlation process is interchangeable and canbe done by adjusting the image to the map or adjusting the map to theimage. In some cases both acquired image and dust map should be adjustedto some common ground. Such an example may happen when the map iscalculated based on a aperture that the lens does not reach or adifferent lens than the one used with different optical configuration.Alternatively, such as in the case of a new lens, this process (300) ascalled by 130, may be used to adjust the map onto a new map and fromthat stage onwards continue with a single map.

If no dust map corresponds with the image (140), a new dust map iscreated (200). When a dust map does correspond (140) to the image, thepreferred embodiment checks if the dust specs as defined in the dust mapare of high enough confidence level to being dust regions (150). Thestatistical decision as to the way such confidence level is calculatedfor the dust map in general and for the individual dust specs, isfurther discussed in FIG. 2 and FIG. 3. If the confidence level is low,the image is added to the updating of the dust map (200). If after theimage is added, the confidence level is high enough (152) the softwarecontinues to the dust removal process (160). Otherwise, the softwareprogresses to the next image (170).

For example, a dust map is considered valid after 10 images areanalyzed, and a dust spec is considered valid after a dust is detectedin 8 images. In this case, after analyzing 9 images, the software maycontinue to the stage of updating the dust map (200) but upon completion(10 images) there is a valid dust map, and the software will continue tothe correction (160) stage. If however the loop (110) is only on its1^(st) to 8^(th) image, no correction will be done.

As an additional embodiment, images can be corrected retroactively afterthe dust map reached high enough confidence. This can be used for batchprocessing or off line processing or processing where the information isgathered in parallel to the needed correction. In this embodiment, whenthe confidence level is not enough (152, NOT-YET) the images, a pointerto them, or a list of them, or a representation of them, that were usedto create the dust map are stored in temporary location (154) and whenthe dust map is ready (151—YES), the software will retroactively removethe dust from all those images (156). In this fashion, all images,including ones that originally did not hold sufficient statisticalinformation, may be corrected.

Referring to dust detection and correction (160), this process may beexecuted as a loop on every dust spec in the dust map, with a stage ofdetection and correction (400, followed by 166 and 168). Alternatively,the process can be implemented where all dust specs are detected first(162) and then all dust specs are corrected (164). The decision as tothe sequence of operations varies based on implementation criteria suchas what regions of the image are in memory, and should not affect thenature of the preferred embodiment. As part of the detection, thesoftware also performs a self testing (500) where each new imageintroduced is compared to the dust map. This process is further definedin FIG. 5. The importance of this stage for each dust spec and for thedust may, is that in this manner, if the dust situation changes, such asa single spec moving aground or the camera being serviced), the softwarewill immediately detect the change and re-validate the dust map. Asdescribed above, the validity test (500) can be implemented on a dustspec by dust spec or on the full dust map.

Referring to FIG. 2-a, dust map creation and updating is illustrated.This process can receive a collection of images as defined by FIG. 1.blocks 108 and 109) or one image at a time is refereed to this process,as defined by FIG. 1. block 110.

If the function is called with a single image (220—SINGLE IMAGE), theimage is directly provided to the calculations (270). If multiple imagesare provided (240 MULTIPLE IMAGES), then an initial step is to define ifthere are more than enough images for defining the map. This step isdesigned to optimize the creation process for dust in cases of a largeamount of images.

The sequence of the images are to be referenced based on the originalcollection of N images as defined in FIG. 1 blocks 102, 103 or 104. Thesequence of images is based on a few criteria such as: giving moreweight to images shot last, and if images are shot in a relatively smalltime frame, allocation in the sequence to movements of objects overlarge distances to try and assure minimal repetitiveness between similarimages that may have been taken of the same object with little movement.The sequence will not be limited to the number of images (HIDP) becauseit may well be that some regions will not have enough data in them toevaluate the dust. This may happen in cases where part of the image isvery dark in some of the images.

As an example: if N (number of images in a selection)=30; and HSdp(number of images needed to determining map)=10; and all images wereshot in a space of an hour; then a potential sequence may be:

30, 27, 24, 21, 18, 15, 12, 9, 6, 3, 29, 26, 25 . . . , 2, 28, 25, . . .1

Alternatively if the same 30 images were taken over a period of a monthit may be beneficial to select images sequentially (last one shot is thefirst to be calculated):

30, 29, 28, . . . 20, 19 . . . 2, 1

And in some cases this process of sampling the series (270) may alsodecide not to use images that are taken too long from the last image. Inthis case, for example if image 1-15 were taken in July and 16-30 weretaken in November, this process may limit the new map to 16-30 or evencreate two different maps, one for images 1-15 and the other for 16-30.

In a different criteria, the parameters as extracted from the imageswill determine the sequence and the number of dust maps that are to becalculated. For example if a folder contains N=30 images, where 15 weretaken with one camera and 15 with another, the sampling step (270) maycreate two map sets.

Another criteria for creating a new set or checking for new dust is thetype of lens. If a lens is changed, it means that the CCD-cavity wasexposed to potential new dust. This may trigger a new set of images tobe looked at. It may also be an indication that the camera was serviced,or that the photographer cleaned the camera. Of course, if there is aparameter that defines when a camera was serviced, this will trigger thecreation of a new dust map.

Those familiar in the art may be able to determine the rightcombinations of creating this sequence based on the nature of the dust,the camera and the lens. The next loop (270-271) defines the marking ofeach region and the addition of the region to the dust map if it is notalready there. There are three type of regions in an image, the firstare images with sufficient information to detect whether they are of thenature of dust, e.g., dark regions surrounded by a light background.Other criteria may be regions with a relatively small color saturation.The second group are regions that are very probably non-dust. Suchregions are for example all clear, or of high color saturation. Otherregions are inconclusive such as a very dark segment of the image. Inthis case, it will be hard to detect the dust even if it was part of theimage. Alternatively, when looking for over-exposed or “dead pixels”,the criteria may be reversed, if the pixels appear as a white spec inthe image.

The criteria may be also a function of the acquisition parameter. Forexample an image with a open aperture may all be marked as in-decisive,because the dust may not appear on the image.

Regions that are potentially dust are marked (292) and then added to thedust mask (294). The addition may be the creation of a new dust spec onthe map or the modification of the probability function or theconfidence level counter for the region. Regions that are most likelynon-dust are marked (282) and then added to the dust mask (284). Theaddition may be the creation of a new dust spec on the map or themodification of the probability function or the confidence level counterfor the region. The additions of the regions needs to be normalized tothe shooting conditions as defined by the dust map (300) if this stepwas not performed prior to entering this function, as optionally definedin FIG. 1.

This loop continues over all regions of the image (271). Alternatively(272), each region is compared (500) with the map dust to se if there isno case where the monotonicity is broken, i.e. a region that was of highprobability to be dust is now non-dust.

FIG. 2-b describes an alternate embodiment of a dust creation process.

Block 1210 describes the preparation of the dust map which includeseither opening an existing map 1216 or creating a new one 1214, whereall pixels as a starting point are non dust or WHITE.

After the map is correlated to the shooting conditions, 300, a dust mapI-dM is created in block 1220.

All pixels in the image, 1222, receive the following values 1224 basedon the luminance value of the pixel:

If luminance is less than DARK_THRESHOLD, then I-pM (X,Y)=MAYBE_DUST;

If luminance is greater than WHITE_THRESHOLD, then I-pM(x,y)=WHITEPIXEL;

OTHERWISE I-pM(x,y)=DON'T_KNOW.

Once all pixels are analyzed, 1220, they are then clustered, 1296 intodust regions or dust specs in a I-pM dust map.

The next step is to create a dust map dM which is continuous based onthe value of the individual pixels. In the final stage 1250, the dustmap is threshold by the predetermined value THRESHOLD to create a binarymask.

FIG. 3 illustrates the process of correlating the image to a defaultsettings of the dust map. This process defines correlating the image ofthe dust map, the dust map to a new dust map of the dust map to themage. In particular this correlation refers to the adjustment of theshooting conditions to some accepted standard. The acquisitionconditions in particular refer to the aperture and the focal length. Thecorrelation process is interchangeable and can be done by adjusting theimage to the map or adjusting the map to the image. In some cases bothacquired image and dust map may be adjusted to some common ground. Suchan example may happen when the ma is calculated based on a aperture thatthe lens does not reach or a different lens than the one used with adifferent optical configuration. Alternatively, in case of a new lens,this process (300) may be used to adjust the map onto a new map and fromthat stage onwards continue with a single map.

To begin with, the dust map is being loaded (112) and the default dataon which the map was generated is extracted (310). Such data may includethe lens type, the aperture and the focal length associated with thedefault state. In concurrence, the information form the acquired image(304) is extracted (320) and compared to the one of the dust map.

As explained in the mathematical model of the optical system, the twomain adjustments between the dust map and the image are based on focallength, and on aperture, each creating a different artifact that shouldbe addressed. Knowledge of the phenomena may assist in creating a betterdetection and correction of the dust artifact. Alternatively, in aseparate embodiment, analysis of the image and the modification of thedust as changed by aperture and focal length, may provide themathematical model that describes a transformation that defines changesto the dust as a function of change in lens type, focal length andaperture.

The mathematical distortion of the dust as a function of the aperture isillustrated in FIG. 7 a-7 f. The geometrical optics illustrations of theabove phenomena are depicted in FIGS. 6 a-6 e. Referring to FIG. 3,after extracting the data, the following step is modification of the mapand or the image based no focal length (900), and based on aperture(800). The following steps are further defined in FIG. 9 and FIG. 8respectively.

Following the steps (800 and 900) the Image and the Dust Map areconsidered to be correlated. The correlated map cM is no longer binarybecause it defines both the shift and the fall off which is continuous.FIG. 400 defines the process of detecting and removing the dust from theimage. The input is the image I is loaded, if it is not already inmemory (404) and the correlated dust map is cM is loaded (402) if notalready in memory.

The process of detecting and removing the dust is done per dust spec.This process is highly parallelized and can be performed as a singlepath over the image, or in strips. The flexibility of performing theoperation on the entire image, or in portions, combined with thecorrelation or as a separate process, enables a flexible implementationof the algorithm based on external restrictions defined by the hardware,the run time environment, memory restrictions and processing speed.

As defined and justified by physical phenomena, a method of correctingdust artifacts is described based on two different operations. Theformer is the retouching or the in-painting here regions with no data(420), or data that is close to noise to be recreated as defined in 430and later on in FIG. 7 e, 7 f. The second portion of the correction isbased on the tapering degradation of surrounding pixels as a function ofthe aperture, as illustrated in FIGS. 7 b, 7 c, 7 d.

Referring to the image enhancement portions, where the data exists butmost likely not in its full form, due to the fact that some of the dustaffects the quality of the image, but some regions still contain somedata (420), an image enhancement algorithm is performed on the pixels(430). In a simplified embodiment (432), assuming that the optical modelis simplified to a degradation in the overall brightness as defined bythe OPACITY, the enhanced pixels will receive a value inversely relatedto the OPACITY i.e. 9432)

${I^{\prime}\left( {x,y} \right)} = \frac{I\left( {x,y} \right)}{OPACITY}$

To maintain a check of the validity of the model, the pixels beforebeing operated on may be provided for validation (500) as described inFIG. 5. The second portion of the image correction is the restoration orthe inpainting (460). In this case, the area behind the dust has norelevant data to enhance, or if there is, this data is relatively closeto the overall noise level and thus can not be enhanced. Therefore,there is a desire to in-paint every pixel based on the analysis of thesurrounding region to the dust (470). In the case where the enhancementregions as defined in block 430 are of good quality, those pixels aswell may contribute to the in-paining. Otherwise, they are excluded formthe calculations. The decision may rely on the distance of the pixels tothe OPAQUE ones, of the minimum level of OPACITY that was used torestore the pixels in block 430. The larger the OPACITY, the smallersuch pixels may be relied on in the inpainting process.

FIG. 4 b illustrates an embodiment of the in-painting process. Ingeneral, each pixel in the obscured region, 480 is to be filled, 482,based on its surrounding pixels. In this specific embodiment, the pixelsare filled-in based on information of the surrounding non-affectedpixels. This specific algorithm takes into account that the pixelsclosest to the periphery have a better chance to be anticipated by theexternal pixels. Therefore the process is done from the outside inwards.

This process of spiraling inwards is also depicted in FIG. 4 d. In it,given a dust spec 1400 in a grid 1410, the dust takes a digital form ofthe surrounding bounding area 1420. External pixels such as 1430 are notpart of the dust region, while internal ones such as 1450 are.

An algorithm that works on the periphery moving inwards is describedwith reference to FIG. 4 b. Block 470 is depicted in FIG. 4 d asfollows: In the first round all peripheral pixels, numbered form 1 to 20are being operated on as defined in FIG. 4 b, block 474. After that, allof the above mentioned twenty pixels, as defined in FIG. 4D block 1460are removed, according to block 476 of FIG. 4 b, and a region is formedleaving a smaller dust spec of shape 1470. This modified dust spec has adifferent set of peripheral pixels numbered 21-31. After removing thosepixels by the in painting process, block 467, a smaller dust kernel asdepicted in 1480 is left with only three pixels 34, 35 and 36.

The process of filling in the pixels need not be spiral. In a differentalternative, the process follows the pattern of the region surroundingthe dust. For example lines and edges, or other high frequencyinformation are being filled in prior to filling in the smooth regions.This approach will prevent unnecessary blurring due to the in-paintingprocess.

In a preferred embodiment, a criteria for the chosen value can be basedon marinating the overall gradient around the pixel 462. Thejustification is that in the case of a steep edge, it is not advisableto copy information for the surrounding pixels with the edge value. Bydoing so, the in painting process will maintain any high frequencyinformation in the picture such as lines and edges.

An illustration of that is given in FIGS. 4 c, 4 d and 4 e. Referring toFIG. 4 c, the same dust 1400 as in FIG. 4 b with the bounding box 1420on a grid 1410 is obscuring a picture including high frequency data suchas the letter A, 1440, by taking a small section of based on 9 pixels asdepicted in FIG. 4 d pixel 1490 is surrounding by 8 pixels 1491, 1492,1493, 1494, 1495, 1496, 1497, 1498.

In a simplification, each pixel receives the average value between theblack and white regions. This is depicted in FIG. 4 e. In this case, thepixel 1490 and the surrounding 8 pixels 1491, 1492, 1493, 1494, 1495,1496, 1497, and 1498, have a digital value of 21, 220, 250, 245, 253,180, 145 and 35 respectively. It is clear that the best value of pixel1490 will come form its surrounding pixels with the smallest gradient.Because in practice the value of pixel 1490 can not be determined, butis the center of the in painting, the value of the gradient will bebased on the value of the gradients of the pixels around it andextrapolated to this pixel.

In this specific example, the differential horizontal gradient betweenpixels 1497 and 1493 is the largest while the gradient vertical gradientof 1495 and 1491 will most likely be the same. Therefore, a preferredvalue of 210 will be based on the extrapolated average of the twogradients of its top and bottom pixels.

FIG. 500 describes a tool that may be used in various stages of theprocess, namely quality control. This process can be called from themain workflow (FIG. 1) the creation of the dust map (FIG. 3) or theimage restoration and enhancement (FIGS. 4 and 4- a respectively).

A quality check may be performed to assure that pixels will not bewrongly classified, nor mistakenly corrected when they should not.

The quality control test can be applied to a pixel in an image whichbelongs to a potential dust (510). In case the image has not yet beencorrelated with the dust (300), this process should then be done. Thenext step is to check whether the pixel belongs to a dust region or not.For example, in a small aperture, the region behind the dust should beclose to if not totally obscured. If not (530 NO), there is a remainingdesire to revive the dust map (550) or the image does not correspond tothe dust map. This can happen when the image is from a different time,or from a different acquisition device. In this case, the software willcreate a new dust map (200) to correspond to the new dust or lackthereof, or inform the user that it cannot correct this image. In casewhere there is not enough information (530 MAYBE), there is noconclusive evidence to reject the correlation and thus the processcontinues (580) with no action. In the case that the image displaysinformation that may concur with the dust map, the software may continue(580) or prior to that, enhance the likelihood in the dust map (200)that the region is indeed dust.

FIG. 8 describes the adjustment of the dust map to the image acquisitionparameters based on the aperture. Simplifying, the closer aperture is,the crisper and more noticeable the dust is. In other words, forexample, for images taken with an f-stop of f-32, the dust will be veryprominent and opaque, while the same image taken at f-2.8 may display novisual degradation of the image.

The correction of the image should take that information into account,to prevent over-correction of the dust artifact.

The acquisition information and the corresponding dust map default setupare extracted in blocks 326 and 312, respectively. Then, for each dustspec in the image 810, the size of the region that is still obscured bythe dust is calculated, as defined by mathematical model. In some cases,when the aperture is very open, this region may decline to 0. In others,where the aperture is still very close, the size may be close to thesize of the dust. Alternatively, this step, 820, may be done as apreparation stage, and kept in a database, which can be loaded.

The process then splits in two. The fully obscured region will be markedin 834 pixel by pixel 832 in a loop 834, 835 and will be treated by thein-painting process as defined in FIG. 4-a. A semi-opaque dust map iscreated in the loop 840, 841 for each pixel. Each of the pixels 842 isassigned an OPACITY value 844, based on the mathematical model asdescribed previously in FIG. 7 a-4 d. The dust spec that is onlypartially attenuated will go through an inverse filtering of theinformation already there, as described in FIG. 4 block 430, with aspecific embodiment in block 432. The process of the inverse filteringmay take into account the signal to noise ratio to avoid enhancing datawhich is not part of the original image. For example, the region aroundthe dust may have an over-shoot similar to a high pass filter, which maymanifest itself in the form of an aura around the dust. This aura shouldto be taken into account before enhancing the regions.

FIG. 9 describes the adjustment of the Dust Map based on the Focallength, and the specific lens. The scientific background is explained inFIGS. 7 e-7 f. As described before, the shift of the dust spec as afunction of focal length for a specific lens is a function of equation13 the thickness of the window—tw, which is constant for a given cameraand exit pupil position—Pe which varies based on the lens system and thevariable focal length in case of a zoom lens.

Given an image and a dust map, the pertinent information is loaded, asdescribed in FIG. 3, namely the focal lens and lens type of the camera,326, the focal length and lens type in the dust map 312 and the cameradistance of dust to the sensor 318.

The process then goes through the dust specs in the image 910 andcalculates the shift of the dust as explained in FIG. 7 a-7 e. Thecoordinates of the pixel are calculated from the center of the opticalpath, 922, and the shift is calculated 924. Alternatively to goingthrough each pixel, in order to speed the process, only the periphery ofthe dust spec can be calculated and the rest will be filled in.Moreover, because the shift is a function of the location (x,y) of thedust, in the case where dust is far enough from the origin, the dustshape will not change. It is then sufficient to calculate only a shiftof a single point and displace the entire dust spec accordingly. Theregions, which are only partially attenuated due to the change inaperture, may be calculated in this stage 940, 941, if calculatedalready as illustrated in FIG. 8, or alternatively, the displacement canbe calculated first as explained in blocks 942,944.

In some cases, it is impossible to get data on the exit pupil, or thedistance the dust is from the sensor. Such cases may be when theapplication has no a-priori knowledge of the camera or the lens that wasused.

It is still possible in those cases to create a reasonable dust map, byempirical reconstruction of the parameter based on analysis of theimages, the shift in the dust and the falloff of the dust edges. Suchtechniques are defined in FIGS. 10 and 11 illustrating a process ofestimating, based on empirical data, the values of the parameters in theformulae that defines the change in dust as a function of change inaperture.

This process can be useful in the case that the software has no a-prioriknowledge of the extracted parameters of the camera or lens that areused to convert the acquired image and the dust map image into the sameknown space. In an alternative embodiment, this technique can also beused to extract optical parameters, similar to methods done in acontrolled laboratory settings such as using an optical bench of a lensregardless of the desire to remove dust artifact from an image.

Alternatively, this process can be used with partial knowledge, such asthe shift of a single dust spec to evaluate the transposition of alldust specs in the image.

FIG. 10 defines the process of creating the mathematical formulae basedon empirical data to parameterize the change in dust as a function ofchange in focal length.

In general, a proposed embodiment relies on the fact that when dust isfound, a pattern matching can be applied to find the shift in the dust.Based on this information,

$\frac{t_{w}}{P_{e}}$can be calculated as defined in Equation 13-a. If t_(w) is known then Pecan be calculated as recited in equation 1-b.

Specifically, in a preferred embodiment, an image is acquired, 1010 anda dust map is calculated 1012. A second image is captured, 1030 with adifferent focal length than the first image, and a dust map iscalculated 1032. The process repeatedly tries to find two dust spots inthe two dust maps 1040. If no dust specs are correlated, the process isrepeated for consecutive images 1020.

The process of finding dust specs is calculated by applying a localcorrelation to each of the dust specs. Preferably, based on Equation13-a, the further the dust is from the center, the better the precisionis.

When two specs are determined to be from the same dust spec, thedisparity between the specs is calculated 1042. The ratio between theshifted pixels is calculated. This ratio is the numerical empiricalestimation of t_(w) in equation 13-a. Moreover, if the distance of thedust to the sensor is known, the exit pupil of the lens can becalculated based on the same equation.

FIG. 11 illustrates a process of estimating based on empirical data thevalues of the parameters in the formulae that define the change in dustas a function of change in aperture.

The process is similar to the one described for estimation of the focallength, albeit the parameters calculated are different.

Specifically, a first image is acquired, 1110 and dust is detected, 1120in this image. If the image is not appropriate for detecting the dust,or if the probability is low for the dust regions, this image isrejected for this purpose and another image is chosen. For the empiricalcomparison, a second image is captured 1140, or alternatively a set ofimages 1130, all with varying aperture, to enable acceptable samplingset. The process then looks for a detected dust region with high levelof probability. In the case that all other parameters are similar exceptthe aperture, the process can search for dust regions in the samecoordinates that the original image dust regions were found. The dustregions of the two or more images are correlated 1160. The processcontinues for a sufficient amount of dust regions, 1168, which in somecases can even be a single one, and sufficient amount of images, 1169,which can also be, depending on the confidence level, a single image.Once the dust regions are correlated 1160, the fall off due to thechange of aperture is calculated, 1172, on a pixel by pixel basis, 1170,for every pixel in a dust region, 1179. Based on this information, thefall-off function is calculated. 1180. In a preferred embodiment, thefall-off function is determined as a function of the distance of a pixelfrom the periphery of the dust, as well as the aperture.

Alternatively, the dust specs may also be determined by trying tocorrelate the dust spec in the map to the acquired image. Suchcorrelation can be performed within a reasonable window size or even onthe diagonal line between the dust and the center of the optical path,in the direction that the dust may move. By gaining knowledge on themovement of a single dust spec, as explained in formulae 13a-13d, allother dust specs shift can be determined.

It is also possible to determine whether the camera should be physicallycleaned based on analysis of the dust in the camera and the specificdust patterns. This is illustrated in the flowchart of FIG. 12. Anexample will be that a certain width of dust will not allow correctin-painting based on the surroundings. Another example will be theoverall number of dust specs or the overall relative area that the dustcovers. The input for such analysis is a dust map, 1200. This map can besimilar to the dust map generated in block 200, or any otherrepresentation of a dust map or a calibration map, generatedautomatically or manually by the photographer. Such analysis need not beperformed for every image. A process, 1210 determines whether to performsuch analysis. Examples to trigger this process are the time since thelast analysis, change of lenses, which may create the introduction ofdust, or message from the quality control of dust map, as defined inFIG. 5 block 500, that the dust has shifted or that the dust no longercorresponds to the map. In general, any changes in the dust structuremay be a justification to trigger the analysis process. When no analysisis desired, 1212, the process terminates. Otherwise, the analysis isperformed, 1220. The analysis is performed for each dust specindividually, 1130, and then the results are accumulated for the wholeimage. For each dust region, 1140, some parameters are being extracted,including, but not limited to: area of dust region, maximum width ofdust region; distance between dust region and neighboring regions;movement of dust region from last analysis; and occurrence of new dustspecs since last analysis. Following this analysis, the results aresummarized to include, e.g., overall area of dust, in size and inpercentage for the entire image, largest width of dust, largest area ofdust spec, changes in area of dust since last analysis, and changes ofdust particles since last analysis. In an alternate embodiment, eitherautomatically or based on the photographers preference, this analysismay be displayed or saved in a log file for future reference 1221. Eachof the aforementioned criteria may have an acceptability thresholdvalue. This threshold value is determined empirically by themanufacturer in terms of the maximum acceptable dust that can becorrected in software. Alternatively, this data may be adjusted by thephotographer based on her tolerance level to dust. If any of theparameters exceeds an acceptable threshold, the user is informed, 1290,that the camera should be manually maintained and cleaned up.

Alternatively, 1285, this same process may be used as a tool to informthe user of changes in the dust. Such information is particularlyimportant in the case that the dust correction algorithm is based on thecreation of a calibration image. In this case, the analysis will be usedto inform the user that a new calibration image should be acquired tosupport the correction of dust in future images.

Alternatively, the process of analysis described above may also beincorporated in a maintenance procedure, where the camera, after beingcleaned up will perform an auto-test, as described in FIG. 12, to verifythat the camera now is indeed clean. In such cases, the thresholdparameters are substantially more restrictive and demanding, to assurehigh quality maintenance.

There are many alternatives to the preferred embodiments described abovethat may be incorporated into a image processing method, a digitalcamera, and/or an image processing system including a digital camera andan external image processing device that may be advantageous. Forexample, an electronic circuit may be designed to detect maximum andminimum dust detection probability thresholds while acquiring pixels inan image (see also U.S. Pat. No. 5,065,257 to Yamada, herebyincorporated by reference). Such a circuit can produce signals that maybe used in processing to eliminate regions, which lie outside theexpected range of signal values due to the presence of dust particles orsimilar optical defects, or alternatively to accept, maintain oreliminate regions as dust artifact regions based on whether aprobability determination exceeds, high or low, a certain threshold orthresholds. A technique may be used to detect and provide a remedy forthe effects of dust on a digitally-acquired image (see also U.S. Pat.No. 5,214,470 to Denber, hereby incorporated by reference). An image maybe recorded within a digital camera or external processing device suchas may be signal coupled with a digital camera for receiving digitaloutput image information or a device that acquires or captures a digitalimage of a film image. The digital image may be compared with the filmimage, e.g., through a logical XOR operation, which may be used toremove dust spots or blemishes picked up in the acquisition of thedigital image from the film image.

Multiple images may be processed and stationary components, which arecommon between images, may be detected and assigned a high probabilityof being a defect (see also U.S. Pat. No. 6,035,072 to Read, herebyincorporated by reference). Additional techniques, which may be employedto modify defect probability, may include median filtering, sample areadetection and dynamic adjustment of scores. This dynamic defectdetection process allows defect compensation, defect correction andalerting an operator of the likelihood of defects.

Dark field imaging may be employed to determine the location of defectsin digital images from digital cameras or film scanners (see U.S. Pat.No. 5,969,372 to Stavely et al., and U.S. patent application2001/0035491 to Ochiai et al., each hereby incorporated by reference). Anormal imaging of a object with normal illumination may be followed by asecond imaging using different wavelengths, e.g., infrared illumination.Dust, fingerprints, scratches and other optical defects are typicallyopaque to infrared light. Thus the second image produces an image withdark spots indicating the position of dust particles or other defects.

A process may involve changing any of a variety of extracted parameters(see elsewhere herein), angle of sensor relative to image plane,distance of image plane or sensor from dust specks (e.g., on window ofsensor), etc., and imaging a same object with the digital camera. Acomparison of the images reveals with enhanced probability the locationsof dust artifact. In a camera application, the unique location of theactual dust relative to the object and to the image plane provideinformation about extracted parameter-dependent characteristics of dustartifact in the images. The analysis for the digital camera applicationdepends on the “transmission”-based optical parameters of the system,i.e., the fact that light travels from a scene through the camera lensand onto the camera sensor, and not involving any substantial reflectiveeffects. It is possible to make determinations as to where the dustactually is in the system by analyzing multiple images taken withdifferent extracted parameters, e.g., on the sensor window, or in animage of an original object which itself is being images such as in filmimaging.

In a scanning application, this technique can be use the face that aspeck of dust will cast a shadow of a different color, geometrylocation, etc. with changes in extracted parameters, e.g., with adifferent color with increasing elongation of the shadow for eachparallel row of pixels (a “rainbow” shadow, as it were). Multiple scanstaken from various angles of illumination may be employed to produce animage which identifies dust defects from their shadows and the colorsthereof (see U.S. Pat. No. 6,465,801 to Gann et al. and U.S. patentapplication 2002/0195577 and 2002/0158192 to Gann et al, herebyincorporated by reference). A linear scanning element moves across adocument (or the document is moved across the scanning element) and animage of the document is built up as a series of rows of pixels. Thisdiffers from the physical configuration of a camera in which a shutterilluminates a X-Y sensor array with a single burst of light. In bothcases, though, dust may lie close to the imaging plane of the sensor.

Technique may be applied as part of a photofinishing process toeliminate blemishes on a film image obtained by a digital camera (seealso U.S. patent application 2001/0041018 to Sonoda, hereby incorporatedby reference). Such techniques may import previous acquired informationabout defects in images from a blemish detection procedure. A techniquefor correcting image defects from a digital image acquisition devicesuch as a digital camera may involve repeated imaging of an object orother image, where each successive image-acquisition involves differentproperties or extracted parameters or meta-data related properties, suchas variable angles of incidence or variable lighting or contrastparameters, and the results of these repeated scans may be combined toform a reference image from which defect corrections are made (see alsoU.S. patent application 2003/0118249 to Edgar, hereby incorporated byreference). A decision on whether a defect in an image acquired by afield-based digital camera is to be corrected or not may be based on abalancing of considerations. For example, the likely damage tosurrounding defect-free portions of the image may be balanced againstthe likelihood of successfully achieving correction of the defect.

Image processing means may be employed where the detection or correctionof defects in a digital image may be based solely on analysis of thedigital image, or may employ techniques directly related to the imageacquisition process, or both. Anomalous image regions may be determinedbased on the difference between the gradient of an image at a set ofgrid points and the local mean of the image gradient (e.g., see U.S.Pat. No. 6,233,364 to Krainiouk et al., hereby incorporated byreference). Such technique can reduce the number of false positives in“noisy” regions of an image such as those representing leaves in a tree,or pebbles on a beach. After determining an initial defect list by thismeans, the technique may involve culling the list based on a one or moreor a series of heuristic measures based on color, size, shape and/orvisibility measures where these are designed to indicate how much ananomalous region resembles a dust fragment or a scratch.

Techniques and means to correct scratches in a digitized images mayemploy a binary mask to indicate regions requiring repair or noiseremoval, and sample and repair windows to indicate (i) the regionrequiring repair and/or (ii) a similar “sample” area of the image (seealso U.S. Pat. No. 5,974,194 to Hirani et al., hereby incorporated byreference). Data from a sample window may be converted to a frequencydomain and combined with frequency domain data of the repair window.When a low-pass filter is applied, it has the effect to remove thesharp, or high-frequency, scratch defect.

Techniques and means of detecting potential defect or “trash” regionswithin an image may be based on a comparison of the quadraticdifferential value of a pixel with a pre-determined threshold value (seeU.S. Pat. No. 6,125,213 to Morimoto, hereby incorporated by reference).The technique may involve correcting “trash” regions within an image bysuccessively interpolating from the outside of the “trash” region to theinside of this region.

Techniques and means to automate the removal of narrow elongateddistortions from a digital image may utilize the characteristics ofimage regions bordering the distortion (see also U.S. Pat. No. 6,266,054to Lawton et al., hereby incorporated by reference). User input may beused to mark the region of the defect, or automatic defect detection maybe employed according to a preferred embodiment herein, while theprocess of delineating the defect is also preferably also performedautomatically.

Techniques and means to allow automatic alteration of defects in digitalimages may be based upon a defect channel having a signal proportionalto defects in the digital image (see also U.S. Pat. No. 6,487,321 toEdgar et al., hereby incorporated by reference). This allows areas ofstrong defect to be more easily excised without causing significantdamage to the area of the image surrounding the defect.

Techniques and means may be employed to generate replacement data valuesfor an image region (see also U.S. Pat. No. 6,587,592 to Georgiev etal., hereby incorporated by reference). Image defect may be repaired asfacilitated by the replacement data. Moreover, the repairing of theunwanted image region may preserve image textures within the repaired(or “healed”) region of the image.

Techniques and means may be employed to detect defect pixels by applyinga median filter to an image and subtracting the result from the originalimage to obtain a difference image (see also U.S. patent application2003/0039402 and WIPO patent application WO-03/019473, both to Robins etal., each hereby incorporated by reference). This may be used toconstruct at least one defect map. Correction of suspected defect pixelsmay be achieved by replacing those pixel values with pixel values fromthe filtered image and applying a smoothing operation. User input may ormay not be utilized to further mitigate the effects of uncertainty indefect identification.

Techniques and means for retouching binary image data which is to bepresented on a view-screen or display apparatus may be employed toeliminate local screen defects such as dust and scratch artifacts (seealso U.S. patent application 2002/0154831 to Hansen et al., herebyincorporated by reference). The production of visible moiré effects inthe retouched image data may be avoided by the replacement of smallareas.

A digital video camera with sensor apparatus may incorporate a defectdetecting mode (see also U.S. Pat. No. 5,416,516 to Kameyama et al.,hereby incorporated by reference). The locations of detected defectpixels may be retained in the memory of the camera apparatus andreplacement pixel values may be interpolated by processing algorithms,which convert the sensor data into digital image pixel values.Techniques may be employed to automatically detect and compensate fordefective sensor pixels within a video camera (see also U.S. Pat. No.5,625,413 to Katoh et al., hereby incorporated by reference). The cameramay perform a dark current measurement on start-up when the camera irisis closed and by raising the gain can determine pixels which exhibitabnormally high dark current values. The location of these pixels isrecorded in camera memory as a LUT with associated threshold brightnessvalues associated with each pixel depending on its dark current value;defect compensation depends on input image brightness and ambienttemperature.

An image pickup apparatus, such as a digital camera, may have adetachable lens (see also U.S. patent application 2003/0133027 to Itoh,hereby incorporated by reference). The camera may incorporate a defectdetecting section and a compensation section for sensor defects. Furtherthe defect detection operation may become active when the camera lens isdetached so that the user will not miss an opportunity to take a picturedue to the operation of the defect detection process.

The techniques of the preferred and alternative embodiments describedherein may be applied to printers and to imaging devices such as digitalcameras which incorporate a focusing lens system. A process may beemployed for detecting and mapping dust on the surface of a photographicelement (see also U.S. Pat. No. 5,436,979 to Gray et al., herebyincorporated by reference). This may be applied in the context of averification procedure to follow a cleaning process for a range ofphotographic elements including film negatives and slides. Statisticalinformation may be obtained and presented to an operator to allowcontrol of the cleaning process. Detailed location information may bealso recorded and/or correction means may be also provided for dustdefects on a photographic element.

Techniques and means to create a defect map for a digital camera orsimilar imaging device may use an all-white reference background (seealso U.S. patent application 2002/0093577 to Kitawaki et al., herebyincorporated by reference). The location of any dust or scratch defectsmay be recorded in the memory of the imaging apparatus when the camerais in a dust detection mode and when a dust correction circuit is activeany image data co-located with a defect may be corrected for thepresence of dust by elimination, color correction or interpolation basedon the surrounding pixels. Further, where the position of a dust defectchanges with f-stop of the camera a list of dust locations correspondingto f-stop settings is pre recorded at the time of manufacturing in a LUTin the camera memory. Any effect of different focal length may besimplified to the effect of the change in dust due to magnification ofthe lens. In addition, techniques for dynamically obtaining a defect mapbased on the processing of a plurality of images may be employed withthis technique.

Techniques may be also employed involving correcting for dust defectsbased on the geometry of said dust or of the camera. Further techniquesmay involve utilizing camera metadata to enhance the detection andcorrection processes for defects. Further techniques may involvealerting the user that the camera requires servicing due to excessivelevels of dust contamination, or the fact that it is not onlymagnification but the actual lens that is mounted.

A method of filtering dust artifacts form an acquired digital imageincluding multiplicity of pixels indicative of dust, the pixels formingvarious shapes in the image, may be employed. The method may includeanalyzing image information including information describing conditionsunder which the image was acquired and/or acquisition device-specificinformation. One or more regions may be determined within the digitalimage suspected as including dust artifact. Based at least in part onsaid meta-data analysis, it may be determined whether the regions areactual dust artifact.

A method may include obtaining a dust map based on analysis of multipleimages acquired by the same image acquisition device. The dust map mayinclude regions of various shapes and sizes indicative of statisticallyrecurring patterns associated with dust.

A method may further include analyzing the images in comparison to apredetermined dust map to establish the validity of the dust overprogressions of time. The method may further involve mapping theacquired image to a predetermined default acquisition condition as afunction of the lens type and the focal length that was used atacquisition.

A method may further include mapping a dust spec as depicted in the dustmap and the suspected dust specs in the acquired image based on acalculated transformation of the dust as a function of the lens and theaperture, or other extracted parameter, used to acquire the image. Theactual removal of dust artifacts from an image may include a step wheremissing data as obscured by the dust specs is regenerated and in-paintedbased on analysis of the region in the image surrounding the dust spec.The actual removal of the dust artifacts from the image may also includea step where deteriorated regions primarily in the periphery of the dustspec are enhanced and restored based on knowledge of the deteriorationfunction. The actual image retouching may include both in-painting andrestoration or either one of these operations, or another imagecorrection technique as may be understood by those skilled in the art.

A method of detecting and removing dust artifacts may be performed inthe acquisition device as a post-processing stage prior to saving theimage. This method may further include an analysis of the image in itsraw format immediately followed by the acquisition stage. The method ofdetecting and removing dust artifacts can be performed on an externaldevice as part of a download or capture process. Such external devicemay be a personal computer, a storage device, and archival device, adisplay or a printing device or other device. The method of detectingand removing dust artifacts can be performed in part in the acquisitiondevice and the external device.

A dust detection and/or correction technique may be applied post priorito a collection of images, or individually to images as they are addedto a collection. The map may be generated a priori to the introductionof an image, or dynamically and in concurrence to the introduction ofnew images. The method may further include steps of providing astatistical confidence level as to the fact that a certain region isindeed part of a dust spec. The method may further provide tools todetermine whether the acquisition device may benefit from somemaintenance.

A method may be employed that may be implemented as part of adigitization process, such as correcting defects on scanning device,whether flat bed or drum, whether for hard copy documents or for filmdigitization. A method may be further applied to other recurring imageimperfections such as dead pixels on the sensor, burnt pixels on thesensor, scratches, etc. A method of automatically determining whether torecommend servicing a digital image acquisition system including adigital camera based on dust analysis may be advantageously employed. Amethod of calculating parameters of an optical system may be based onanalysis of the dust.

While an exemplary drawings and specific embodiments of the presentinvention have been described and illustrated, it is to be understoodthat that the scope of the present invention is not to be limited to theparticular embodiments discussed. Thus, the embodiments shall beregarded as illustrative rather than restrictive, and it should beunderstood that variations may be made in those embodiments by workersskilled in the arts without departing from the scope of the presentinvention as set forth in the claims that follow and their structuraland functional equivalents.

Particularly, any of the techniques described above or claimed below maybe combined in alternative embodiments with any of the following. Amethod of automatically correcting dust artifact within images acquiredby a system including a digital acquisition device including a lensassembly is provided. The method includes acquiring multiple originaldigital images with the digital acquisition device. Probabilities thatcertain pixels correspond to dust artifact regions within the images aredetermined based at least in part on a comparison of suspected dustartifact regions within two or more of the images. Probable dustartifact regions are associated with one or more values of one or moreextracted parameters relating to the lens assembly of the digitalacquisition device when the images were acquired. A statistical dust mapis formed including mapped dust regions based on the dust artifactdetermining and associating. Pixels corresponding to correlated dustartifact regions are corrected within further digitally-acquired imagesbased on the associated statistical dust map.

The dust artifact probabilities may be determined by statisticallycombining multiple individual probabilities based on each of the regionswithin two or more images. Probabilities may alternatively be determinedthat certain pixels within the image correspond to regions free of dustbased at least in part on a comparison of suspected dust artifactregions within one or more of images. Certain suspected dust artifactregions may be eliminated based on probabilities that certain pixelscorrespond to regions free of dust, and/or as having a determinedprobability below a first threshold value that the suspected region isin fact dust artifact.

Certain further dust artifact regions may be judged as having aprobability above the threshold value, such as to be subject to furtherprobability determining including comparison with further acquiredimages prior to judging whether each further dust artifact region willbe subject to the eliminating operation. There may be only a singlethreshold such that above the threshold, the suspected region will bejudged to be subject to a dust correction operation, or a secondthreshold above the first threshold may be applied for that purpose, andthere may be further thresholds defined within the software.

The probability determining operation may include weighting suspecteddust artifact regions according to one or more predetermined probabilityweighting assessment conditions. These conditions may include size,shape, brightness or opacity, feathering, or peripheral smoothness ofsaid suspected dust artifact regions, or a degree of similarity in size,shape, brightness, opacity or location with one or more suspected dustartifact regions in one or more other images, or combinations thereof.

The one or more extracted parameters may include aperture size,F-number, magnification, lens type, focal length of an optical system ofthe digital camera, or combinations thereof. The one or more extractedparameters may be calculated empirically from comparison of one or moredust artifact regions within multiple original digital images with thedigital acquisition device.

The further digitally-acquired images may include different images thanthe originally acquired images, and may further include one or more ofthe same original images. The different images may be acquired withdifferent values of one or more extracted parameters, they may beacquired of a different object or objects or of a different scene orscenes.

The determining and associating operations may be repeated for thefurther digitally-acquired images, and the statistical dust mapincluding mapped dust regions may be updated based on the additionaldust artifact determining and associating. The determining andassociating may also be repeated for additional images acquired with thedigital camera, and the statistical dust map including the mapped dustregions may be updated based on the additional dust artifact determiningand associating. Pixels may be corrected corresponding to correlateddust artifact regions within the additional images based on the updated,associated statistical dust map. One or more of the further and originalimages may be updated based on the updating of the associatedstatistical dust map. The updating for the further and original imagesmay be limited to updates that do not include appearance of new dust ormovement of existing dust, and/or to updates that include previouslydetermined dust artifact regions.

A version description may be created of changes in the statistical dustmap. One or more of the further and original images may be updated basedon the updating of the associated statistical dust map based on theversion description. The version may be based on a chronological timestamp, and/or replacement of a lens. Version information may include achange of probability in the statistical dust map that certain pixelscorrespond to dust artifact regions. The version information may includeone or more parameters including a change in dust location, change indust position, appearance of a new dust region, and/or a disappearanceof an existing dust region. A determination may be made as to whether adust map is to be replaced based on determining that sufficientdisparity exists based on an amount and/or quality of changes in thestatistical dust map.

The image correction method may be automatically performed within adigital camera that includes an optical system, a sensor array,processing electronics and a memory. The image correction method mayalso be performed at least in part within an external processing devicethat couples with a digital camera that includes the optical system andthe sensor array to form a digital image acquisition and processingsystem that also includes the processing electronics and the memory. Theprogramming instructions may be stored on a memory within the externaldevice which performs the image correction method. The digitalacquisition device may capture images from film images, and the digitalacquisition device may include a digital camera.

The dust artifact probability determining may include dynamicallyupdating the probabilities based on comparisons with suspectedequivalent dust artifact regions within the further digitally-acquiredimages. The determining of probabilities is further based on a pixelanalysis of the suspected dust artifact regions in view of predeterminedcharacteristics indicative of the presence of a dust artifact region.The dust artifact probability determining may include determiningprobabilities that certain pixels correspond to dust artifact regionswithin acquired images based at least in part on a comparison ofsuspected dust artifact regions within two or more digitally-acquiredimages, or on a pixel analysis of the suspected dust artifact regions inview of predetermined characteristics indicative of the presence of adust artifact region, or both.

The probability determining may further include statistically combiningprobabilities based on comparisons of inner or shadow regions and ofaura regions. The probability determining with respect to a shadowregion of a dust artifact may be based on an extractedparameter-dependent shadow region analysis, wherein the shadow regionanalysis presumes that certain regions on a sensor of the digital imageacquisition device are fully obscured by the dust. The probabilitydetermining with respect to an aura region of the dust artifact may bebased on an extracted parameter-dependent aura region analysis, whereinthe aura region analysis presumes that certain regions on a of thedigital image acquisition device are partially obscured by the dust. Theaura region analysis may include calculating effects of differences invalues of the one or more extracted parameters in different images ofdust artifact illumination, shape, position, reflection or transmissionproperties, distance of dust to the sensor, aperture, exit pupil, orfocal length, or combinations thereof. The different images may beacquired with different values of the one or more extracted parameters,and the different images may be acquired of different objects.

The method may further include validating whether a furtherdigitally-acquired image has non-contradicting data that the probabilitythat certain pixels correspond to dust artifact regions within the imageprior to correcting pixels corresponding to correlated dust artifactregions within the images based on the associated statistical dust map.The user may be instructed to create a new dust map if the validatingdetermines a noticeable change in the dust map. The shadow regionanalysis may include calculating effects of differences in values of theone or more extracted parameters in different images on dust artifactillumination, shape, position, reflection or transmission properties,distance of dust to the sensor, aperture, exit pupil, or focal length,or combinations thereof.

Suspected dust artifact regions of the further digitally images mayinclude inner or shadow regions and aura regions. Focal length extractedparameters may be calculated empirically from comparison of thetransposition of inner or shadow regions of dust artifact regions withinmultiple original digital images acquired with the digital acquisitiondevice. Aperture extracted parameters may be calculated empirically fromcomparison of fall off of aura regions of the dust artifact regionswithin the multiple original digital images acquired with the digitalacquisition device. The correcting may include a first correcting of theaura regions and a second correcting of the inner regions, in eitherorder.

The method may be performed on raw image data as captured by a camerasensor. The method may be performed on a processed image after beingconverted from raw format to a known red, green, blue representation.The correcting operation may include replacing pixels within one or moredigitally-acquired images with new pixels. The correcting may includeenhancing values of pixels within one or more digitally-acquired images.Correcting instructions may be kept in an external location, such as animage header, to the image data.

The dust artifact probability determining operation may include loadingthe statistical dust map, loading extracted parameter information of apresent image, performing calculations within the statistical dust maphaving extracted parameter variable-dependencies, and comparing dustartifact detection data with the extracted parameter dependentstatistical dust map data. The extracted parameter information mayinclude values of aperture size, focal length and/or lens typeinformation. The dust artifact probability determining operation mayalso include loading the statistical dust map, loading extractedparameter information of a present image, performing a calculation forrelating the statistical dust map with the present image according to aselected value of an extracted parameter which is otherwise uncorrelatedbetween the present image and the dust map, and comparing dust artifactdetection data with the now correlated statistical dust map data.

Suspected dust artifact regions of at least two images may include inneror shadow regions and aura regions. The comparison may include acomparison of the inner regions and a different comparison of the auraregions, in either order. The dust artifact regions may include an auraregion partially obscured by dust and a shadow region substantiallyobscured by dust inside the aura region.

The determining with respect to a shadow region may be based on anextracted parameter dependent shadow region analysis, wherein the shadowregion analysis presumes that certain regions on a sensor of the digitalimage acquisition device are substantially obscured by said dust. Theshadow region analysis may include calculating effects of differences invalues of the one or more extracted parameters in different images ondust artifact illumination, shape, position, reflection or transmissionproperties, distance of dust to the sensor, aperture, exit pupil, orfocal length, or combinations thereof.

The determining with respect to an aura region may be based on anextracted parameter dependent aura region analysis, wherein the auraregion analysis presumes that certain regions on a of the digital imageacquisition device are partially obscured by said dust. The aura regionanalysis may include calculating effects of differences in values of theone or more extracted parameters in different images on dust artifactillumination, shape, position, reflection or transmission properties,distance of dust to the sensor, aperture, exit pupil, or focal length,or combinations thereof.

The correcting operation may include in-painting or restoration, orboth. The in-painting correcting may be applied to the shadow region.This in-painting may include determining and applying shadow regioncorrection spectral information based on spectral information obtainedfrom pixels outside the shadow region. The restoration correcting may beapplied to the aura region. The restoration may include determining andapplying aura region correction spectral information based on spectralinformation obtained from pixels within the aura region.

In addition, in methods that may be performed according to preferredembodiments herein, the operations have been described in selectedtypographical sequences. However, the sequences have been selected andso ordered for typographical convenience and are not intended to implyany particular order for performing the operations, unless a particularordering is expressly provided or understood by those skilled in the artas being necessary.

Many references have been cited above herein, and in addition to thatwhich is described as background, the invention summary, briefdescription of the drawings, the drawings and the abstract, thesereferences are hereby incorporated by reference into the detaileddescription of the preferred embodiments, as disclosing alternativeembodiments of elements or features of the preferred embodiments nototherwise set forth in detail above. A single one or a combination oftwo or more of these references may be consulted to obtain a variationof the preferred embodiments described in the detailed descriptionabove.

1. A digital image acquisition device, comprising (a) an imageacquisition sensor, (b) a shutter, (c) optical elements for focusing animage on the sensor, (d) an aperture disposed between said opticalelements and said shutter, (e) a translucent lens cap which defocusesimages when in place, (f) digitally-embedded programming such that thedevice is arranged to automatically capture a calibration image of ade-focused scene when said shutter and said aperture are open, and toderive a map of defects from the calibration image acquired by thesensor when illuminated by ambient light, and (g) a trigger forautomatically acquiring a de-focused calibration image which is arrangedto automatically acquire such calibration image for the map of defectsbased on change of lens, amount of images taken, replacement of lenscap, or combinations of these parameters.
 2. A digital image acquisitiondevice, comprising (a) an image acquisition sensor, (b) a shutter, (c)optical elements for focusing an image on the sensor, (d) an aperturedisposed between said optical elements and said shutter, (e) a lenswhich defocuses images when in a dust-detection mode, (f)digitally-embedded programming such that the device is arranged toautomatically capture a calibration image of a de-focused scene whensaid shutter and said aperture are open, and to derive a map of defectsfrom the calibration image acquired by the sensor when illuminated byambient light, and (g) a trigger for automatically acquiring ade-focused calibration image which is arranged to automatically acquiresuch calibration image for the map of defects based on change of lens,amount of images taken, replacement of lens cap, or combinations ofthese parameters.
 3. A digital image acquisition device, comprising (a)an image acquisition sensor, (b) a shutter, (c) optical elements forfocusing an image on the sensor, (d) an aperture disposed between saidoptical elements and said shutter, (e) a translucent lens cap whichdefocuses images when in place, (f) digitally-embedded programming suchthat the device is arranged to automatically capture a calibration imageof a de-focused scene when said shutter and said aperture are open, andto derive a map of defects from the calibration image acquired by thesensor when illuminated by ambient light; and (g) a trigger forautomatically acquiring a de-focused calibration image which is arrangedto automatically detect whether the translucent lens cap is in place asa pre-requisite for triggering capture of the defocused calibrationimage.
 4. The device of claim 3, wherein the trigger is arranged totrigger said capture based at least in part on time interval, change oflens, or amount of images taken, or a combination thereof.
 5. A digitalimage acquisition device, comprising (a) an image acquisition sensor,(b) a shutter, (c) optical elements for focusing an image on the sensor,(d) an aperture disposed between said optical elements and said shutter,(e) a lens which defocuses images when in a dust-detection mode, and (f)digitally-embedded programming such that the device is arranged toautomatically capture a calibration image of a de-focused scene whensaid shutter and said aperture are open, and to derive a map of defectsfrom the calibration image acquired by the sensor when illuminated byambient light, wherein the digitally-embedded programming includes atrigger for analyzing whether the image is sufficiently de-focused as apre-requisite for capture of the de-focused calibration image.
 6. Thedevice of claim 5, wherein the trigger is arranged to initiate captureof a plurality of de-focused calibration images of the scene within acertain time frame.
 7. The device of claim 5, further comprisingvalidating that additional digitally-acquired images havenon-contradicting probability data that certain pixels correspond todust or other blemish artifact regions within said additionaldigitally-acquired images prior to correcting pixels corresponding tocorrelated dust artifact regions within the additionaldigitally-acquired images based on the associated statistical dust map.8. A digital image acquisition device having no photographic film,comprising an optical system, a processor and one or more storagedevices for programming the processor to control the camera to perform amethod of automatically correcting dust artifact regions within acquiredimages, the method comprising: (a) acquiring one or more originaldigital images through a translucent lens cap disposed along an opticalpath between an object and one or more components of the optical systemincluding a digital sensor; (b) determining probabilities that certainpixels correspond to dust or other blemish artifact regions within saidone or more original digital images; (c) associating the dust or otherblemish artifact regions with one or more extracted parameters relatingto the optical system when the one or more original digital images wereacquired; (d) forming a statistical dust map including mapped dust orother blemish regions based on the dust or other blemish artifactprobability determining and associating; (e) correcting pixelscorresponding to dust artifact regions within each of said one or moreoriginal images based on the associated statistical dust map; and (f)triggering an automatic acquisition of a de-focused calibration imageincluding analyzing whether the image is sufficiently de-focused as apre-requisite for triggering capture of the defocused calibration image.9. The device of claim 8, wherein said one or more original imagescomprise original images of de-focused scenes.
 10. A digital imageacquisition device having no photographic film, comprising an opticalsystem, a processor and one or more storage devices for programming theprocessor to control the camera to perform a method of automaticallycorrecting dust artifact regions within acquired images, the methodcomprising: (a) acquiring one or more original digital images through atranslucent lens cap disposed along an optical path between an objectand one or more components of the optical system including a digitalsensor; (b) determining probabilities that certain pixels correspond todust or other blemish artifact regions within said one or more originaldigital images; (c) associating the dust or other blemish artifactregions with one or more extracted parameters relating to the opticalsystem when the one or more original digital images were acquired; (d)forming a statistical dust map including mapped dust or other blemishregions based on the dust or other blemish artifact probabilitydetermining and associating; and (e) correcting pixels corresponding todust artifact regions within each of said one or more original imagesbased on the associated statistical dust map, wherein said determiningprobabilities further comprises statistically combining a plurality ofindividual probabilities based on each said region within two or moresaid images.
 11. The device of claim 4, wherein the method furthercomprises eliminating certain suspected dust or other blemish artifactregions as having a probability below a first threshold value.
 12. Thedevice of claim 8, wherein said one or more extracted parameterscomprise aperture size or focal length or both.
 13. The device of claim8, wherein the method further comprises digitally-acquiring additionalimages with said digital acquisition device, repeating said determiningand associating, and updating said statistical dust map includingupdating said mapped dust or other blemish regions based on theadditional dust or other blemish artifact determining and associating.14. The device of claim 8, the dust or other blemish artifactdetermining including: (I) loading the statistical dust map; (II)loading extracted parameter information of a present image; (III)performing calculations within the statistical dust map having extractedparameter variable-dependencies; and (IV) comparing dust artifactdetection data with the extracted parameter dependent statistical dustmap data.
 15. The device of claim 8, the dust or other blemish artifactdetermining including: (I) loading the statistical dust map; (II)loading extracted parameter information of a present image; (III)performing a calculation for relating the statistical dust map with thepresent image according to a selected value of an extracted parameterwhich is otherwise uncorrelated between the present image and the dustmap; and (IV) comparing dust artifact detection data with the nowcorrelated statistical dust map data.
 16. The device of claim 8, whereinthe method further comprises sorting dust or other blemish artifactdistribution data within said dust map according to meta-data.
 17. Thedevice of claim 8, wherein said digital acquisition device captures saidimages from film images.
 18. The device of claim 8, wherein the methodfurther comprises determining probabilities that certain pixelscorrespond to regions free of dust or other blemishes within said imagesbased at least in part on a comparison of suspected dust artifactregions within one or more of said images.
 19. A digital imageacquisition device having no photographic film, comprising an opticalsystem, a processor and one or more storage devices for programming theprocessor to control the camera to perform a method of automaticallycorrecting dust artifact regions within acquired images, the methodcomprising: (a) acquiring one or more original digital images through atranslucent lens cap disposed along an optical path between an objectand one or more components of the optical system including a digitalsensor; (b) determining probabilities that certain pixels correspond todust or other blemish artifact regions within said one or more originaldigital images; (c) associating the dust or other blemish artifactregions with one or more extracted parameters relating to the opticalsystem when the one or more original digital images were acquired; (d)forming a statistical dust map including mapped dust or other blemishregions based on the dust or other blemish artifact probabilitydetermining and associating; and (e) correcting pixels corresponding todust artifact regions within each of said one or more original imagesbased on the associated statistical dust map, wherein the method furthercomprises judging certain probable dust or other blemish artifactregions as having a probability above a second threshold value such asto be subject to said correcting.
 20. A digital image acquisition devicehaving no photographic film, comprising an optical system, a processorand one or more storage devices for programming the processor to controlthe camera to perform a method of automatically correcting dust artifactregions within acquired images, the method comprising: (a) acquiring oneor more original digital images through a translucent lens cap disposedalong an optical path between an object and one or more components ofthe optical system including a digital sensor; (b) determiningprobabilities that certain pixels correspond to dust or other blemishartifact regions within said one or more original digital images; (c)associating the dust or other blemish artifact regions with one or moreextracted parameters relating to the optical system when the one or moreoriginal digital images were acquired; (d) forming a statistical dustmap including mapped dust or other blemish regions based on the dust orother blemish artifact probability determining and associating; (e)correcting pixels corresponding to dust artifact regions within each ofsaid one or more original images based on the associated statisticaldust map, (f) digitally-acquiring additional images with said digitalacquisition device, (g) repeating said determining and associating, and(h) updating said statistical dust map including updating said mappeddust or other blemish regions based on the additional dust or otherblemish artifact determining and associating, wherein said determiningincludes dynamically updating said probabilities based on comparisonswith suspected equivalent dust artifact regions within the additionaldigitally-acquired images.